Segment Reporting - Reconciliation of Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting [Abstract]
Net loss attributable to common shareholders of Evolent Health, Inc.									$ 301,971	$ 52,658	$ 60,665
Interest income									3,987	3,440	1,656
Interest expense									(14,534)	(5,484)	(3,636)
(Provision) benefit for income taxes									21,536	(40)	6,637
Depreciation and amortization expenses									(60,913)	(44,515)	(32,368)
Impairment									(199,800)	0	0
Loss from equity method investees									(9,465)	(4,736)	(1,755)
Gain on disposal of assets									9,600	0	0
Change in fair value of contingent consideration and indemnification asset									3,997	4,104	(400)
Other income (expense), net									(492)	109	171
Net loss attributable to non-controlling interests	$ 1,197	$ 217	$ 285	$ 1,910	$ 853	$ 126	$ 115	$ 439	3,609	1,533	9,102
ASC 606 transition adjustments									0	(4,498)	0
Purchase accounting adjustments									(1,915)	(861)	(1,467)
Stock-based compensation expense									(15,618)	(17,609)	(20,437)
Severance costs									(17,350)	(2,205)	0
Amortization of contract cost assets									(2,876)	(2,456)	0
Acquisition costs									(10,769)	(2,665)	(15,964)
Adjusted EBITDA									$ (10,968)	$ 23,225	$ (2,204)